Hypertension is the major risk factor for cardiovascular diseases and affects over 70 million Americans. The kidney sets the long-term level of blood pressure by regulation of body fluid volume and ultimately peripheral resistance. Novel strategies to redirect the inappropriate increases in renal vascular resistance and tubular reabsorption address the problem of sustained hypertension. Adenosine is a major regulator of renal control of fluid balance and renal vascular resistance, acting on specific receptors in the proximal tubule and in the afferent arteriole. These two sites of action provide novel and sensitive regulation of fluid balance and have been targeted to manage fluid volume. Adenosine, type 1 and type 2 receptors (A1-AR, A2- AR) have opposing actions in both tissues. Activation of A1-AR constricts the afferent arteriole and promotes Na+ uptake in the proximal tubule. Activation of A2-AR dilates the afferent arteriole and inhibits Na+ uptake in the proximal tubule. Therefore the balance of these actions plays an important role in renal function, but is currently poorly understood. This project will explore the precise roles of each receptor in the uptake of proximal tubule Na+ and fluid and on the setting of renal vascular resistance mediated by tubuloglomerular feedback during two distinct models of hypertension in A1-AR deficient mice. Specific Aim one will test the hypothesis that adenosine-1 receptors in the proximal tubule promote Na+ and volume retention during salt- sensitive hypertension and that adenosine-2 receptors modulate that influence. Proximal tubule reabsorption will be measured by renal microperfusion and recollection techniques and correlated to blood pressure. Specific Aim two will test the hypothesis that adenosine-1 receptors in the afferent arteriole and in the proximal tubule enhances blood pressure increase during angiotensin II-induced hypertension. The role of adenosine-2 receptors as modulators of these effects will also be tested. Proximal tubule reabsorption and tubuloglomerular feedback, measured by renal micropuncture techniques, will be assessed during the early and late stages of hypertension after chronic angiotensin II infusion. In addition, vascular reactivity of afferent arterioles will be contrasted between these two models. Results from these studies will advance our knowledge of adenosine control of renal-dependent blood pressure regulation and identify new targets for therapy.